Sealed variable length cell and positioner



:..SEALED VARIABLE LENGTH CELL AND POSITIONER Filed July 27, 1951 May 5,1953 b. HERBERT 2 SHEETIS-Sl-lEETl nil-hilt lwlllllllllllaxl W I ATTORNEy 5, 9 A. D. HERBERT 2,637,817

SEALED VARIABLE LENGTH GELL ANTEY'PQSITIONER Filed July 2'7, 1951 2SHEETS-SHEET 2 lulllunillllli l N V E N TO R 44 7 90,? a. A/f/PBIA 7',

f4 AM ATTORNEY Patented May 5, 1953 solemn vastnes BOSITIONER} Amineiioasfo; New Brunswick, NZ 1;,

assign to'American.Cyanamid Company New York; Y a. corporation; of.Maine Application Jul y 1951 Seflfl NW.

I 2 Claims; I

This invention relates to a. variable length sealed celLmoreparticularly, a cellsof alkali metal halide" for infrared:spectroscopic: work.

In infrared spectrometers, the length. of path through the'materialto beexamined is often an important factor and is particularly so withliquids. Variable length cells: have been proposed in whichthe-length ofthe cell-is variedbymoving a. piston. These. cells have suffered. fromseveral cl-rawbacks.- The problem-of amovableinirared trans-parentpiston isa seriousone and leakage or sticking due to corrosion hasrendered. the cells short -lived. and, in general; not" verysatisfactory although when. the cell. is new, useful int-raisedspectrograms can be made. H

The, present invention operates on v a different principle, namely-,.that of a wedge in which illumination is transverseof the cell instea'dlof alon the length of the cell. Thev cells of the present invention areprepared easily by holding. together two fi'at plates of suitablematerial, one of the platesor blocks being providedwith a wedgeshapeddepression. For work in the infrared region; these plates may beformedof various alkali metal halides The blocks are contained in a mountingin which they are maintained in contact under spring pressure. The cell.holder can then" be" incorporated suitable" micrometrically movableframeworks" to permit very precise movement of the ce11- across aninfrared beam.

The cells of the present invention possess a number of importantadvantages. place, they are completely sealed and are useful with anytype of liquid, regardless of its volatility. Th thickness of film canbe varied precisely by micrometric movement of the cell across aninfrared beam and the rate at which cell thickness varies with movementcan be changed at will by varyin the slope of the wedge-shapeddepression in one of the two cell blocks. It is thus possible to producecells of any desired wedge angle.

It is of course possible to provide a wedgeshaped depression in each oftwo cell-blocks and these can then be inverted to give a workable cellof much greater variable thickness. This has the advantage of being ableto use thinner cells, resulting in economy of space and expense.

Another important advantage of the cells of the present invention isthat the problem of sealing is completely solved. The spring mountingprovides a tight seal at all times and there is no problem of movingparts which renders the ordinary type of piston cell unsatisfactory.

A further important advantage of the present invention is that the cellblocks are extremely In the first cheap t'o'producei 'liliere. is nonecessity oi special shapes as in cells. with: transparent.v pistom. isan important factor, because the alkali metal halide cells used ininfrared work are extremely sensitive ton'i'oistureand a cell which isrelatively cheap thus rediicesverymaterially replacementc'osts Anotheradvam'iage ofthe cells-of" the; present invention is: that measurementof difier ent film thicknessesoi'. liquids is possible; withoutremovcell'. from. the instrmnent.. Ifhis isanimportant practicaladvantage, as many infiaredinstrumen-ts areeither evacuated; or"pizovided with speciah dehydrated atmosphereswhich make. it undesirableto'open-the machine any more: thanis absolutelyrnecessary. The-fiatwedge-shapedcells of the present inventionlend themselves tomulti-plemounting ,vthus ,-or example, a celleholding framework may carry anumber of cells which can. be introduced successively into the infraredbeam. making it possible to" measure a number of les with?asingleo-pening of the machine. Wit-l the piston of cell .this isdiificult or impossible whereprecise measurement is required.

While the: cells of the present invention are of particular importancein. the measurement of liquids. especially" volatile liquids, they mayalso be used foi measurement" of? solids. especially solidssuch. ascomminut'eds solids which db not lend themselves to the productionofself-supporting shapes. With most solids it is, of course, possible toprepare the solid in the form of a wedge which does not require a. cellof the type covered by the present invention.

The cells of the present invention should not be confused with holdershaving wedge-shaped depression-s which are usable with solids ornonvolatile liquids. The perfect sealing obtained by means of thepresent invention permits handling and measurement in positions whichare not possible with open cells and the present invention is thereforedefinitely limited to sealed cells which can be used in an position. Theinvention will be described in greater detail in conjunction with thefollowing specific examples in which:

Figure 1 of the drawings is a front elevation of my positioning adaptorand cell carrier with the cell in place;

Figure 2 is a top view of my invention with the cell removed;

Figure 3 is an end view of the positioning adaptor illustrated in Fig. lwith the cell removed;

Figure 4 is a view in perspective of the positioning adaptor;

of the cell taken that apparatus for use with thecell-of the presentinvention. The cell is securely held i'n the cell carrier by means ofcell plate 6, Fig. 6, and emachine screws. w

In determining the infrared absorption f a liquid, alkali metal halideblocks at least one of which contains a wedge-shaped depression, areplaced face to face as illustrated in Fig. 7. A lead foil gasket placedbetween the fiat adjacent surfaces of the salt blocks may aid in forminga tight seal, but such a gasket is not required if the contact surfacesof both salt platesare plane and parallel. a g

The entrance and exit to the cell cavity are provided by two modifiedhypodermic 'needles I which are sealed into the cell plate as shown inFigs. and 6. The needles are shaped and so placed that when the cell isassembled both needles communicate with the cell cavity. The advantageof such an arrangement in emptying,

cleaning and refilling the cell will be readily p'erceive'di v Theliquid to be measured may be introduced into the cell cavity by ahypodermic syringe and both the entrance and the exit are then sealedasshown in Fig. 6 by stainless steel plugs I, ground to fit the needlesutilized.

The cell and carrier are then slid into the positioning adaptor asillustrated by Fig. 5 and solids may be melted and poured into the saltblock cavity. When the solid has cooled, the second salt block may beplaced in position and the cell carrier assembled. Higher-melting solidsmay be shaped by grinding methods which are well known.

The mechanical holder and wedge-shaped cell described above enable oneto accurately positionsamples in a light beam normal to the optical axisand accurately measure the absorption of various thicknesses of liquidor solid samples without removing the samples from the instru- -ment.The sample thickness may be easily and rapidly, reproduced by referenceto the micrometer' scale.

My invention is particularly useful in infrared l spectrophotometrysince the sample may be measof the wedge and the micrometer travel.

ured at two thicknesses differing by a known amount, which can becalculated from the slope Absolute data such as cell thickness andabsorption coefiicient may then be readily obtained.

I I claim:

1. A cell capable of transmitting infrared light,

composed of alkali metal halide plates at least one of which contains awedge-shaped depression, said plates being'so assembled that a sealedwedge-shaped cavity is formed; and communieating means'with the apexandbase of said wedge-shaped cavity to permit the introduction andremoval of liquids from said cavity. 2. An apparatus adapted to move asealed wedge-shaped cell horizontally across the entrance slit of aspectrometer, the external face of said cell being maintained at alltimes normal to the optical axis of said spectrometer; which comprises arecessed plate and a cell holder adapted to slide horizontally in saidrecessed plate; a micrometer screw at one end of said recessed platealigned parallel to the direction of motion of said cell holder; andspring loadin means to maintain said cell holder in contact with the endof said micrometer screw.

ARTHUR DONALD HERBERT.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 171,838 Munnich Jan. 4, 1876 7 585,694 Orford July 6, 18972,545,162 Mully et a1 Mar. 13, 1951

